1. Field of the Invention
The present invention relates to a flat panel display device, and more particularly, to an organic light emitting display device that includes a thin film transistor.
2. Discussion of the Related Art
Recently, with the development of information society, flat panel display devices having characteristics such as slimness, lightweight, and low power consumption have been in demand. Among various types of flat panel display devices, liquid crystal display devices and organic light emitting display devices, each of which includes an array of thin film transistors, have been widely commercialized as display devices for televisions, notebook computers, tablet computers or desktop computers, owing to their excellent characteristics of resolution, color display and picture quality. Particularly, organic light emitting display device have received much attention as a flat panel display device for the next generation, owning to such advantages as fast response speed, low power consumption, and excellent viewing angle characteristic based on self-light emission.
FIG. 1 is a circuit diagram illustrating a pixel structure of a general organic light emitting display device.
Referring to FIG. 1, a pixel P of the general organic light emitting display device includes a switching transistor Tsw, a driving transistor Tdr, a capacitor Cst, and an organic light emitting device OLED.
The switching transistor Tsw is switched in accordance with a scan pulse SP supplied to a scan line SL and supplies a data voltage Vdata, which is supplied to the data line DL, to the driving transistor Tdr.
The driving transistor Tdr is switched in accordance with the data voltage Vdata supplied from the switching transistor Tsw and controls a data current Ioled flowing from a driving power Evdd, which is supplied from a driving power line, to the organic light emitting device OLED.
The capacitor Cst is connected between gate and source terminals of the driving transistor Tdr, and stores a voltage corresponding to the data voltage Vdata supplied to the gate terminal of the driving transistor Tdr and turns on the driving transistor Tdr at the stored voltage.
The organic light emitting device OLED is electrically connected between the source terminal of the driving transistor Tdr and a cathode line EVss and emits light depending on the data current Ioled supplied from the driving transistor Tdr.
Each pixel P of the aforementioned general organic light emitting display device controls an amount of the data current Ioled flowing in the organic light emitting device OLED and allows the organic light emitting device OLED to emit light through the driving transistor Tdr depending on the data voltage Vdata, thereby displaying a predetermined image.
However, in the general organic light emitting display device, threshold voltages Vth of the transistors Tdr and Tsw, especially the driving transistor Tdr, are different for each pixel due to non-uniformity caused by the manufacturing processes of the thin film transistors.
Accordingly, in the general organic light emitting display device, reliability of the thin film transistors and the display panel deteriorates due to such an initial non-uniformity of the threshold voltages of the thin film transistors included in each pixel or a shift of the threshold voltages according to lapse of time.